Influence of salicylic acid pre-treatment on cadmium tolerance and its relationship with non-protein thiol production in flax root

Dose-dependent changes in cadmium (Cd) tolerance, non-protein thiol (NP-SH) production and their relationship were investigated in sixteen-day-old flax (Linum usitatissimum L.) seedlings derived from seeds pre-soaked with various salicylic acid (SA) doses and grown hydroponically under increased Cd concentrations (0, 50 and 100 μM CdCl2). The results show that single Cd subjection decreased root elongation as expressed by tolerance index (TI). Moreover, an overproduction of NP-SH was detected in both roots and shoots. These Cd toxicity effects were directly related to the high levels of Cd amounts in flax tissues as expressed by root and shoot Cd bioaccumulation factors (BAF). In addition, Cd-tolerance of roots TI was negatively correlated with changes in root BAF but positively correlated with shoot BAF. However, positive correlation was illustrated between root TI and NP-SH contents. SA considerably reversed the Cd-induced decrease in root growth parameters and TI. Moreover, in Cd-treated plants, SA pre-soaking prevented Cd accumulation in the shoot as consequence of significant decreases in BAF of roots, Cd transport estimated by the translocation factor (TF) and shoot BAF, respectively. Interestingly, SA pre-treatment reduced BAF of roots and shoots, enhanced NP-SH production in roots and decreased it in leaves. These results suggest that SA might play a preventive role in Cd uptake, sequestration and translocation processes based primarily in roots where SA-enhanced NP-SH contribute to the improvement of flax tolerance to Cd stress.Key words: Cadmium, salicylic acid, bioaccumulation, growth, non-protein thiols, Linum usitatissimum

Cellular and signaling mechanisms supporting cadmium tolerance in salicylic acid treated seedlings

This review spotlights on recent indications that recognizes potential cellular mechanisms that may be involved in the tolerance of salicylic acid (SA)-treated seedlings to the presence of cadmium (Cd) in their environment. It appears probable that SA stimulates signaling systems implicated in plant defense-related actions against Cd-induced oxidative stress. These include mechanisms that reduce uptake of metals into the cytosol by extracellular chelation through extruded ligands and binding onto cell-wall constituents. Cellular chelation of metals in the cytosol by a range of ligands (peptides, phytochelatins (PCs)), or increased efflux from the cytosol out of the cell or into sequestering compartments are also key mechanisms improving tolerance. Free-radical scavenging capacities through the activity of antioxidant enzymes or production of peptides and PCs add another line of defense against the toxic effect of Cd. The SA signaling events can be attributed to the extracellular SA perception model in which reactions between SA and apoplastic proteins result in acute oxidative burst under Cd stress

Cadmium stress tolerance in plants: a key role of endogenous and exogenous salicylic acid

Cadmium (Cd) has become one of the major metal stresses which pose a serious threat to plants and animals. In this context, endogenous and exogenous salicylic acid (SA) could play an important role in mitigating the uptake of the Cd ions and providing immunity to plants against the heavy metal stress. SA enhances the resistance capacity of contaminated plants, which, however, depends on the metal concentration and the duration of the treatment. Moreover, SA is considered as a promising signal molecule for improving the efficiency of phytoremediation, and, consequently, growing of safe crops in metal polluted areas. The recent developments in the probable mechanisms by which SA could enhance the tolerance of plants to heavy metals and how it could have an effect on phytoremediation of Cd from contaminated soils are discussed

Exogenous salicylic acid protects phospholipids against cadmium stress in flax (Linum usitatissimum L.)

Salicylic acid (SA) promotes plant defense responses against toxic metal stresses. The present study addressed the hypothesis that 8-h SA pretreatment, would alter membrane lipids in a way that would protect against Cd toxicity. Flax seeds were pre-soaked for 8 h in SA (0, 250 and 1000 µM) and then subjected, at seedling stage, to cadmium (Cd) stress. At 100 µM CdCl2, significant decreases in the percentages of phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylethanolamine (PE) and monogalactosyldiacylglycerol (MGDG) and changes in their relative fatty acid composition were observed in Cd-treated roots in comparison with controls. However, in roots of 8-h SA pretreated plantlets, results showed that the amounts of PC and PE were significantly higher as compared to non-pretreated plantlets. Additionally, in both lipid classes, the proportion of linolenic acid (18:3) increased upon the pretreatment with SA. This resulted in a significant increase in the fatty acid unsaturation ratio of the root PC and PE classes. As the exogenous application of SA was found to be protective of flax lipid metabolism, the possible mechanisms of protection against Cd stress in flax roots were discussed.This research was supported by a Grant no. 2397 from the Ministry of Higher Education, Scientific Research and Technology in Tunisia.Peer reviewe

Salicylic acid improves root antioxidant defense system and total antioxidant capacities of flax subjected to cadmium

Cadmium (Cd) disrupts the normal growth and development of plants, depending on their tolerance to this toxic element. The present study was focused on the impacts of exogenous salicylic acid (SA) on the response and regulation of the antioxidant defense system and membrane lipids to 16-day-old flax plantlets under Cd stress. Exposure of flax to high Cd concentrations led to strong inhibition of root growth and enhanced lipid peroxides, membrane permeability, protein oxidation, and hydrogen peroxide (H2O 2) production to varying degrees. Concomitantly, activities of the antioxidant enzymes catalase (CAT, EC 1.11.1.6), guaïcol peroxydase (GPX, EC 1.11.1.7), ascorbate peroxydase (APX, EC 1.11.1.11), and superoxide dismutase (SOD, EC 1.15.1.1), and the total antioxidant capacities (2,2'-diphenyl-1- picrylhydrazyl (DPPH) scavenging activity and ferric reducing antioxidant power (FRAP)) were significantly altered by Cd. In contrast, exogenous SA greatly reduced the toxic effects of Cd on the root growth, antioxidant system, and membrane lipid content. The Cd-treated plantlets pre-soaked with SA exhibited less lipid and protein oxidation and membrane alteration, as well as a high level of total antioxidant capacities and increased activities of antioxidant enzymes except of CAT. These results may suggest that SA plays an important role in triggering the root antioxidant system, thereby preventing membrane damage as well as the denaturation of its components. © Copyright 2013, Mary Ann Liebert, Inc. 2013.This research was supported by a grant from the Tunisian Ministry of Higher Education, Scientific Research and Technology.Peer Reviewe

Salicylic acid increases tolerance to oxidative stress induced by hydrogen peroxide accumulation in leaves of cadmium-exposed flax

The aim of this study is to investigate the impacts of exogenous salicylic acid (SA) pretreatments on hydrogen peroxide (H2O2) accumulation, protein oxidation, and H2O2-scavenging enzymes in leaves of Cd-treated flax seedlings. Cdenhanced H2O2 levels were related to increased activities of guaiacol peroxidase (POX, EC 1.11.1.7) and ascorbate peroxidase (APX, EC 1.11.1.11), and were independent of changes in catalase (CAT, EC 1.11.1.6) and superoxide dismutase (SOD, EC 1.15.1.1) activities. In control flax seedlings, exogenous SA pretreatments inhibited the activity of CAT, resulted in an enhanced production of H2O2 suggesting that SA requires H2O2 to initiate an oxidative stress. However, although leaves of Cd-free flax seedlings pretreated with SA accumulated in vivo H2O2 by 1.2-fold compared with leaves of Cd-only exposed ones; the damage to growth and proteins after the exposure to Cd was significantly less, indicating that SA can regulate the Cd-induced oxidative stress. Moreover, the Cd-treated seedlings primed with SA exhibited a higher level of total antioxidant capacities and increased activities of H2O2-detoxifying enzymes.This research was supported by a grant from the Tunisian Ministry of Higher Education, Scientific Research and Technology, and the Doctoral School of the Faculty of Sciences of Tunis.Peer reviewe